The invention concerns an open-end spinning apparatus with a spin rotor, the shaft of which is radially supported by an aerostatic radial bearing with an air gap between the bearing assembly and the shaft. The invention further concerns the aerostatic radial bearing for this purpose.
In the case of a known open-end apparatus (JP 57-27212 B2), the shaft of a spin rotor is respectively held in radial bearings in the areas of its forward and rear ends. Through the bearing surface of the radial bearing, compressed air is introduced from the rear area thereof through openings in the direction of an air gap situated between the bearing surface of the radial bearing and the bearing surface of the spin rotor. In normal operation, this aerostatic radial bearing makes possible a bearing for a spin rotor which is free from abrasion and friction.
During operation of open-end spin rotors, however, severe running conditions sometimes occur in such a manner, that an impact between the shaft and the bearing surface happens. These severe running conditions are caused, for example, by imbalance in the spin rotor due to worn drive belts or a jointure in the drive belts. A contacting between the bearing surface of the shaft and the bearing surface of the radial bearing does not necessarily mean a failure of the bearing in service or that the aerostatic radial bearing is immediately unusable because of the contacting.
Therefore, it is a principal purpose of the invention to improve an open-end spinning apparatus and the associated radial bearing in such a manner, that the operational life of the radial bearing is substantially increased. Additional objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
This principal purpose is achieved by having in the case of the bearing surface pairing of the bearing surface of the spin rotor and the bearing surface of the radial bearing, at least one of the bearing surfaces is made from a basic material of polyimide or aramid.
The use of a high temperature resistant plastic substance in the bearing surface makes possible, upon a tilt of the spin rotor and a touching of the two bearing surfaces, a resilient damping. Thereby, the contact of the rotor shaft on the radial bearings does not lead to such a hard impact of the rotor against the radial bearing that damage would be caused to the shaft or the bearing. An aramid, in a particular para-aramid, is installed here, for example, either pure or as a fiber composite. The material can be found from commercial sources, for instance, under the market name Kevlar(copyright).
By the use of the materials polyimide or aramid, a material pairing is obtained, which has a low friction value, is not temperature sensitive, and is particularly resistant to mechanical loading. Polyimides or aramids make available a radial bearing with a high structural and tensile strength for the bearing material, including the bearing surfaces. Besides the favorable frictional characteristics, advantageously, a particularly pronounced ability to withstand mechanical loading also is made possible, especially by the resistance to wear of the materials, polyimide or aramid. By this means, the negative effects of mechanical contacts between the bearing surface of the spin rotor and the bearing surface of the radial bearing are essentially lessened.
These bearing materials, moreover, are in a position to easily resist mechanical loads on the bearing. This is true, not only during operation, but, for example, also during the installation of the spin rotor in the radial bearing in which the air gap between the bearing surfaces allows only a minimal amount of play. By this characteristic, manufacturing errors are reduced and likewise, a contribution to the improvement of the bearing is made. These advantages also become evident, if one or both bearing surfaces are coated with a polyimide or aramid, which acts in a manner corresponding to the above.
Moreover, the materials are readily workable, whereby the retaining of dimensional tolerances during the manufacturing is assured. This workability advantageously also provides that the durability of the bearings is improved, since a precise construction in accord with the design specifications can be carried out simply and safely.
Because the spin rotor is subjected to continuous, extreme loading, abrasive wear does occur in spite of the high resistance of the materials polyimide or aramid to abrasion and their high degree of wear resistance. Where the use of the materials in the bearing surfaces of the spin rotor is concerned, on account of this possible wear, it is advantageous to design the bearing surfaces so that these are removable from the spin rotor and by means of a new coating or by a new bearing installation can be effectively replaced. It is advantageous, when employing these materials in the bearing surfaces of the radial bearing, to provide an insert, which carries the radial bearing surface. This insert can be a releasable holding means, serving as an exchangeable component.
In an advantageous improvement of the invented radial bearing, the polyimide or aramid material possesses a particularly favorable additive, this being graphite, Teflon(copyright), molybdenum disulfide or a mixture of these.
Favorably, the portion of this additive lies between 10 and 45%, preferably more than 20%. Thereby, a particularly lower friction factor of the bearing material is achieved, allowing the wear by mechanical contact between the bearing surfaces again to be reduced. In regard to the use of favorable basic materials for the bearing surfaces, full recognition is given to U.S. Pat. No. 6,401,444 B1, which corresponds to Application No. DE 100 14 861.
By the use of porous materials for bearing surfaces, compressed air can be introduced from the outer circumference of the bearing surface through the porous channels in the material toward the bearing gap between the bearing surfaces. The porous material assures a uniform distribution of the air input without further work-up of the bearing surface material being necessary. For instance, the porous material can be sintered out of polyimide powder with or without the above mentioned additives. Simultaneously, the porous material acts as a throttling device for the application of the air flow into the air gap. In regard to the characteristics of the porous material and the throttle device, examples can be seen in Application DE 100 62 106.
Alternatively, or additionally, to the porous channels in the porous material, in one or both of the bearing surfaces, several borings can be provided. Through these borings, the compressed air is introduced from the rear side to the air gap. For uniform distribution of the air in the air gap, the outlet openings of the borings are advantageously axially aligned and so placed that they are also circumferentially offset from one another. If, instead of borings, micro-openings are employed, then the compressed air entering the air gap can be very precisely adjusted. Additionally, the air flow through the micro-openings is minimal, so that, upon any axial deviation of the rotor shaft toward the radial bearing, the position-restoring air flow, i.e., the compressed air, cannot be forced back into the inlet openings. This air flow markedly increases the rigidity of the bearing. In regard to the formation of the micro-openings and their distribution over an area, particularly on the bearing surface, examples can be seen in DE 100 62 106.
For an additional increase of the operational life of the radial bearing, a material-pairing is employed in the case of the two opposed bearing surfaces in which the material of the one bearing surface is a hard material, or is coated therewith, so that practically no erosion occurs even by touching against an oppositely situated bearing surface, which contains polyimide or aramid.
In accord with another embodiment, in addition to the radial bearing, an axial bearing is installed to serve as an aerostatic axial bearing with an air gap between a bearing fixture thereon and the shaft end of the spin-rotor. The placement of the bearing surface pairing between the axial bearing apparatus and the shaft end or a confronting device on the shaft end, such as a disk, corresponds to the already described bearing surface pairing between the bearing surface of the spin-rotor and the bearing surface of the radial bearing. In this way, a lubrication-free bearing system is achieved for the axial bearing, and consequently, the operational life of this bearing is also extended. In regard to the placement of the aerostatic axial bearing, again examples can be seen in DE 100 62 106.
With the aid of the drawings, embodiment examples of the invention are explained in the following.